Gradient-index Lens Array Research Articles

Application of projection lithography using a gradient-index lens array and wet etching to texturing for control of the hydrophobic properties of stainless-steel plates

The effectiveness of line-and-space (L&S) textures grooved onto stainless-steel SUS 304 plates for improving hydrophobic properties was investigated. The textures were grooved using a scan-projection exposure system with a gradient-index lens array as a projection lens and wet chemical etching in ferric chloride aqueous solution. The lithography system was applied because it was developed for printing rough patterns of larger than 15 μm in a large exposure field of 50 mm square. On the other hand, it was expected that textured protrusions with considerably sharper peaks might be formed by the undercut phenomenon during wet etching. When the contact angles of 2 μl pure-water droplets which had been dropped down onto 20 μm L&S textures were measured, it was found that contact angles measured by observing a droplet from the L&S direction were larger than those measured from the direction perpendicular to the L&S, and contact angles were changeable by grooving textures of different sizes.

High resolution Shack-Hartmann sensor based on array of nanostructured GRIN lenses.

We present a novel method for the development of a micro lenslets hexagonal array. We use gradient index (GRIN) micro lenses where the variation of the refraction index is achieved with a structure of nanorods made of 2 types of glasses. To develop the GRIN micro lens array, we used a modified stack-and-draw technology which was originally applied for the fabrication of photonic crystal fibers. This approach results in a completely flat element that is easy to integrate with other optical components and can be effectively used in high refractive index medium as liquids. As a proof-of-concept of the method we present a hexagonal array of 469 GRIN micro lenses with a diameter of 20 µm each and 100% fill factor. The GRIN lens array is further used to build a Shack-Hartmann detector for measuring wavefront distortion. A 50 lens/mm sampling density is achieved.

Directional Difference of Patterns Printed by Scan-Projection Lithography Using a Gradient Index Lens Array

Peculiar patterning characteristics of scan projection lithography using a gradient index lens array were investigated. When a lens array with two-line lenses was used, pattern widths of line-and-space patterns differed according to the pattern directions. Parts of the light rays diffracted in the direction perpendicular to the lens line are lost without passing through the lenses, because only two lenses are available in that direction. As a result, the resolution of patterns parallel to the lens line slightly degrades. On the other hand, light rays parallel to the lens line are sufficiently used for imaging. For this reason, the widths of line patterns printed in a positive resist slightly decrease. However, if the two-line lens array was replaced by a four-line lens array, the peculiar patterning characteristics were almost lost, and patterns were printed almost without directional differences. This is because the lens array width becomes sufficient.

Optical design in illumination system of digital light processing projector using laser and gradient-index lens

A novel structure of illumination system based on laser sources and gradient-index (GRIN) lens arrays for single-plate digital light processing (DLP) projector is proposed. Under the evaluation of light collection efficiency and illumination uniformity, we designed two different architectures of GRIN lens arrays: the unit lens cross section being either square or circular. Also, we designed the one-to-one coupling mechanism between GRIN lens array and Gaussian beam array. By means of three-dimensional modeling and ray tracing, we simulated the optical characteristics of illumination system, and the optical parameters are evaluated. Results show that the total light collection efficiency is 37.9%, the illumination uniformity is 89.7% and the volume is only 12.4 cm3. Thus we improved optical characteristics and reduced the physical dimension of DLP optical engine.

11.1: An Auto‐Stereoscopic 3D Display Using Tunable Liquid Crystal Lens Array That Mimics Effects of GRIN Lenticular Lens Array

AbstractA tunable liquid crystal lenticular lens array is proposed to compose an auto‐stereoscopic 3D display. The focusing can be achieved based on non‐uniform phase retardation across the width of the LC lenticular lens, mimicking the effects of gradient index (GRIN) lens. The viewing distance and zones of this display can be adjusted in an on‐line fashion to track the viewer position relative to the display. The proposed scheme can present the lenticular lens and the LC GRIN lens simultaneously, so that the simulation results can express the low value of crosstalk of 9% by the lenticular lens array and the LC GRIN lens array.

Resolution analysis of a gradient-index rod and a gradient-index lens array

The physical optics analysis of a gradient-index (GRIN) rod and a GRIN lens array with aberrations is presented. We investigated the optical path length and aberration of a GRIN rod without definition of the stop plane. We also defined an effective aberration transmission function to include aberrations into physical optics analysis. Our theoretical results of impulse responses agree excellently with experiments. For a single GRIN rod, we obtained a theoretical value of 10.3 microm and an experimental value of 10.4 microm for the full width at half-maximum of the intensity point-spread function. For a GRIN array, the theoretical value of 19.2 microm and the experimental measurement of 19.9 microm agree to within 4%. This physical optics methodology with aberrations included can be applied to optical design software. The resolution difference in xerographic process for test material along the "parallel-to-perpendicular" directions is observed. It agrees with the theoretical result for the intensity impulse response of the GRIN array calculated with a second-order correction.

GRIN lens and lens array fabrication with diffusion-driven photopolymer

We introduce a new method to make gradient index (GRIN) lenses and GRIN lens arrays by exposing diffusion-driven photopolymers using a low-power CW laser. By changing the size and power of the laser beam and the exposure time the index profile of the GRIN lens can be controlled. Combined with the self-developing nature of the photopolymer, this enables rapid "on-demand" printing of arbitrary micro-optics. We also introduce a new form of scanning phase microscopy that is conveniently integrated into the lens exposure hardware, providing accurate process monitoring.

Novel Projection Exposure System Using Gradient-Index Lens Array

A novel low-cost projection exposure system for printing rough patterns with a width of approximately 10 µm was proposed and its feasibility was verified. In the novel exposure system, a gradient-index (GRIN) lens array was used as the projection optics. The GRIN lens array projects the same-size erect image of the mask patterns onto the wafers. Therefore, arbitrary patterns on a large mask are replicated on a wafer without using a large projection lens by simply scanning the lens array across the whole mask field. Optical lithography for printing rough patterns with widths of 1–10 µm in large areas is widely applied in fabricating various micro-mechanical components. Since the production volumes are usually small, however, expensive optical lithography systems are not easily adopted for production. The new exposure system will provide new advantages for such lithography applications. When the GRIN lens array was fixed steady, line-and-space (L&S) patterns with a line width of 20 µm were printed in spite of the guaranteed low resolution specification of approximately 80 µm. In addition, up to 2.5 µm L&S patterns were locally resolved. Localized high resolution and the uneven resolution performance mainly depend on the periodical light intensity distribution corresponding to the lens array structure. This intensity distribution was greatly improved by scanning the lens array in the direction of the lens array, and averaging the intensity irregularity. By improving the light intensity distribution to be homogeneous, 10 µm L&S patterns were uniformly printed in the whole exposure area.

Optical shifter for a three-dimensional image by use of a gradient-index lens array.

We propose a new function of the two-dimensional lens array that is composed of many gradient-index lenses. The array forms three-dimensional (3D) images. The characteristics of the 3D images depend on the length of the gradient-index lens. Especially, if the length of the lens is an odd-integer multiple of the half period of the optical path, 3D images are pseudoscopic with a reversed depth. The two lens arrays are positioned at a suitable distance, so that orthoscopic 3D images with the correct depth are formed in front of the lens array.

Three-dimensional video system based on integral photography

A three-dimensional (3-D) video system based on integral photography is proposed. In this system, real erect images of an object are formed by a gradient-index (GRIN) lens array as elemental images and are directly captured by a television camera. A large-aperture convex lens is introduced in front of the GRIN lens array to control the depth range of the reproduced image. The video signal of a group of elemental images is transmitted to a display device that combines a liquid crystal panel and an array of convex microlenses, producing a color 3-D image in real time. As a result, full-color and autostereoscopic 3-D images with full parallax can be observed. We confirmed the possibility of a 3-D television system.

Gradient-index lens-array method based on real-time integral photography for three-dimensional images

Because a three-dimensional (3-D) autostereoscopic image can be seen from a desired viewpoint without the aid of special viewing glasses, integral photography (IP) is an ideal way to create 3-D autostereoscopic images. We have already proposed a real-time IP method that offers 3-D autostereoscopic images of moving objects in real time by use of a microlens array and a high-definition television camera. But there are two problems yet to be resolved: One is pseudoscopic images that show a reversed depth representation. The other is interference between the element images that constitute a 3-D autostereoscopic image. We describe a new gradient-index lense-array method based on real-time IP to overcome these two problems. Experimental results indicating the advantages of this method are shown. These results suggest the possibility of using a gradient-index lens array for real-time IP.

Laser microsoldering of tape‐automated bonding leads using an Nd:YAG laser end‐pumped by a laser diode bar with gradient index lens array coupling

A laser soldering of tape-automated bonding (TAB) leads is tried with a diode-pumped Nd:YAG laser. A 15-W laser diode bar, a multistripe monolithic laser diode array, is used to end-pump Nd:YAG. Twelve beams emitted from 12 stripes, center-to-center spaced 800 mm, of a 1-cm linear diode array were collimated by a lens array of width 1 cm, consisting of 12 gradient-index (GRIN) lenses with 800-mm width, to pump the Nd:YAG facet. The maximum Nd:YAG output power at 1064 nm of 6.3 W is obtained in cw operation. The Nd:YAG laser beam is focused to a spot with a FWHM diameter of 112337 mm. A TAB device with 215-mm-width leads, center-to-center spaced 430 mm, is success- fully soldered by 98-ms irradiation of the laser power of 5.8 W/lead. Soldering is tried with a fiber-coupled Nd:YAG output as well. © 1996 Society of Photo-Optical Instrumentation Engineers.

Gradient-index rod lens with a high acceptance angle for color use by Na^+ for Li^+ exchange

The relationship between the characteristics of gradient-index rod lenses obtained by ion exchange and their mother glass compositions is studied. It is observed that Li(2)O content, R(2)O (Li(2)O + Na(2)O) content, and the Li(2)O/Na(2)O ratio are important factors in attaining a high acceptance angle and a small field curvature. Thus the gradient-index lens array is fabricated by the use of a newly developed glass composition and its optical performance; the modulation transfer function, luminous intensity, and chromatic aberration are precisely evaluated. The array is found to have a sufficiently high performance to be applicable for color use.

Ion beam assisted deposition of a thin film coating on a gradient-index lens array

A new coating method which employs ion bombardment has been developed for a gradient-index (GRIN) rod lens array using silicone rubber and fiber reinforced plastic plates in its construction. The thin film coatings deposited using this method passed the durability tests on the basis of MIL-M-13508C. The adhesion of the thin film coating was strong and durable enough to allow for use on GRIN rod lens arrays in photocopiers. The effect of ion bombardment has been investigated with thin film analysis data by Fourier transform infrared microspectroscopy and secondary ion mass spectrometry.

Gradient‐Index polymer materials and their optical devices

AbstractA gradient‐index (GRIN) plastic optical fiber was prepared by a heat‐drawing process of the GRIN preform rod obtained by a new interfacial‐gel copolymerization technique. The attenuation loss of the GRIN fiber was 179 kB/km at 650‐nm wave‐length and its numerical aperture was 0.20‐0.25. To attain low loss and highly dense integrated circuits, steric radial‐GRIN optical waveguide components such as GRIN branching, star coupler, multi‐coupler, and a 2‐D GRIN lens array, were monolithically fabricated by this technique. A novel spherical GRIN sphere lens, whose index function is symmetrical about the center of the sphere, with a low spherical aberration, was prepared by a modified suspension polymerization technique. A W‐shaped GRIN sphere has been newly proposed to further reduce the spherical aberration, compared with the parabolic GRIN sphere previously proposed.

New interfacial-gel copolymerization technique for steric GRIN polymer optical waveguides and lens arrays

A new interfacial-gel copolymerization technique is proposed to prepare steric gradient-index (GRIN) optical waveguides and lens arrays. Since the GRIN profile is obtained from the thin-gel phase formed on the wall of a polymer substrate, many geometrical GRIN materials, such as axial-, radial-, and spherical-GRIN, can be monolithically fabricated. In this paper the principle of GRIN formation is clarified, and a few steric radial -GRIN circuit components are demonstrated.

Radiometric analysis of gradient-index lens arrays for reduction/enlargement

Gradient-index lens arrays that make reduced or enlarged images have been invented at Xerox Corp. An important optical property of these lens arrays is their radiometric speed. Thus a general procedure for the radiometric analysis of arbitrary magnification gradient-index lens arrays has been developed. The analysis has been applied to a particular array which was fabricated by Nippon Sheet Glass Co. and tested at Xerox.

Reduction/enlargement gradient-index lens array

A novel concept of a gradient-index lens array for reduction and enlargement is described. The array is composed of radial gradient-index rod lenses arrayed in a fanlike manner. Design and radiometric equations are presented. Some image aberrations are discussed in a qualitative fashion. The imaging performance and radiometric properties of a sample lens array are given.

Luminous intensity of a gradient-index lens array

The illuminance of a gradient-index lens array is analyzed theoretically, and some examples of the design of a line scanning optical system are discussed.